A certain document discloses a system for causing plural clouds to be cooperated. More specifically, a cloud cooperation server is provided in each cloud, and the cloud cooperation server of a primary cloud transmits management information concerning resources of the primary system to a cloud cooperation server in a secondary cloud in advance. Then, when the primary system becomes down, the cloud cooperation server of the secondary cloud secures resources based on the management information that has already been received, and then activates a secondary system on the secondary cloud.
This document discloses only simple switching of systems, and does not suppose a case where any trouble occurs in the secondary cloud while the primary system is operating in the primary cloud, or a case where the primary cloud returns after switching the system to the secondary system in the secondary cloud. Because such cases are not supposed, even when the availability of the system becomes high, a phenomenon that the extra resources are wastefully secured may occur.
Patent Document 1: International Publication Pamphlet No. WO 2012/176337
In other words, there is no conventional art for releasing resources that were secured for the redundancy early.